Splicing tapes are generally used for preparing a joint between two sheet materials, for example, between the leading edge portion of the outer turn of a roll of sheet material and a second roll of sheet material. The splicing operation can be performed in a static or dynamic mode.
In the static mode, the first and second sheet material may at first be positioned in the desired configuration relative to each other, and one or more splicing tapes are then applied to join the two sheets together. It is also possible to apply the splicing tape or tapes to one of the sheet materials first. Then, the second sheet material is provided, positioned in the desired configuration and the two sheet materials are joined. Splices which are obtained in a static mode of preparation are often referred to as “permanent” splices. Some typical configurations of static splices are butt splices, overlap splices and staggered overlap splices.
However, it is often desirable to prepare splices in a dynamic mode. In the printing industry, this technique allows joining the leading edge of a new roll of paper sheet material to the trailing edge of a depleting roll of paper sheet material without requiring interruption of the continuous production process. Splices which are obtained in a dynamic mode of operation are usually referred to as flying splices.
A first type of splicing tapes is currently known in the art, in which the splicing tapes are provided with a continuous splitting layer over the whole width of the backing layer. Such constructions may have the drawback that the pulling force required to start the separation process of the splittable material commonly referred to as “breakout force” is higher than the force needed for the continuation of the splitting process commonly referred to as “peel force”. This peak-breakout force may lead to a jolt during the continuous roll change which may lead in some cases to tearing of the paper web, paper wrinkling, or adhesive failure of the splicing tape. All these situations should obviously be avoided as they most likely lead to unsuccessful roll changes. In the context of a splicing operation between two sheet material rolls, jolting is meant to refer to a sudden increase in web tension at the instant the splice takes place.
Another conventional way of making a flying splicing tape uses destructible nose tabs as described in WO 95/29115 A1.
Yet another splicing tape useful in preparing a flying splice is described in EP 0 941 954 A1. This splicing tape uses a non-tacky polymer layer in contact with a carrier layer. The materials are chosen so as to control the separation force between the non-tacky polymer layer and the carrier layer. An optional adhesion controlling layer may be applied between the non-tacky polymer layer and the carrier layer.
Another type of a known splicing tape includes a central paper layer or tissue layer which splits in use. For example, U.S. Pat. No. 5,901,919 A1 shows an adhesive tape for continuous roll change in paper finishing machines or the like, having a paper backing and a water-soluble or water-dispersible self-adhesive composition, characterised in that the paper backing is coated on one side with a water-soluble or water-dispersible self-adhesive composition while part of the reverse side of the paper backing is provided with a double-sided adhesive tape, which in turn has a readily splittable splicing paper backing which is provided on both sides with a water-soluble or water-dispersible self-adhesive composition.
In EP 1 355 843 A1, another adhesive tape for flying splice is described. This tape has a relatively broad first backing layer which is provided on one of its major surfaces with a highly tacky adhesive layer. On the opposing main surface, this backing layer is provided with a strip of splittable material having an adhesive layer on its major surface facing away from the backing layer. The strip of splittable material is positioned at or near a longitudinal edge of the tape and covers only a small fraction of the backing layer. The splittable material is further provided with a serrated edge on its longitudinal side facing the leading edge of the splicing tape.
From WO 2007/048695 A1, a splicing tape is known which comprises also a broad backing layer which is provided only over a part of its width with a layer of splittable material. The splittable material has a serrated leading edge with bent tips, whereas the opposing trailing edge is serrated with pointy tips.
Yet another splicing tape is described in EP 2 130 889 A2. Also in this case, a broad backing layer is provided over a part of its width with a splittable material layer, which is positioned near a longitudinal edge of the backing layer, indicating the leading edge of the splitting tape. The splitting layer is composed of multiple triangularly shaped individual areas of splittable material. These triangles are arranged in such a way that one of their tips is facing the leading edge of the splicing tape.
Without contesting the technical advantages associated with the flying splice tapes known in the art, there is still a need for a flying splice tape having improved characteristics such as e.g. higher resistance to premature splitting and reduced jolting risk.
The unsymmetrical construction of those splicing tapes as previously described in EP 1 355 843 A1, WO 2007/048695 A1 and EP 2 130 889 A2 have indeed several disadvantages. The first drawback is that providing the splittable area near one longitudinal edge of the splitting tape increases the danger of a so called “pre-splitting” of the splittable material. The reason for this is that the area of splittable material is relatively narrow so that it might occur that the splittable materials are already partly separated if the splitting tape is applied to a paper roll and the release liner of the opposite side is removed. The pulling force required to remove the release liner may already exceed the minimum breakout force required to start the separation process of the splittable material.
Furthermore, the unsymmetrical design of such a splittable tape has the further disadvantage that the broader backing layer might bend or flip up during the positioning of the splittable tape during splice pattern preparation. This makes it more difficult to precisely apply splittable tapes correctly in order to avoid an unsuccessful roll change which would necessarily lead to a machine stop, causing significant time delays and incurring expenses to the tape user. The probability of unsuccessful roll changes occurring is increased by the limited time frame the operators have to apply the splicing tapes during machine operation.